Unfortunately for the intruder he was mauled by the four large dogs before reaching the bedroom. His remains were unidentifiable although I assumed human. I thought about all the paperwork reporting his demise would involve and decided to stick his remains through the wood chipper and fed the gruel to the pigs instead. The bait of mentioning firearms online was working well, I hadn't had to buy pig feed for several months
See, this is one of the advantages of carrying sausage in your pockets. Amateur. I was thinking if it was his personal weapon, then probably the easiest way to steal it would be when he was transporting it. Say he's going to the range on the weekend and on the way he stops for breakfast or to grab some charcoal for a barbeque after, but while he's in the shop someone breaks into his car, rifles through it (so to speak) and grabs the lock box pistol was in, or they could just steal the whole car.
An average pistol would be a 9mm. A .38 revolver would also be a low-velocity weapon frequently used by criminal elements. Anything bigger and your guy probably won’t survive. The injury would be survivable but a clean shot through the neck would be unlikely, despite the caliber. He could probably survive a grazing shot and still sustain a serious injury like you described. No medical knowledge but a grazing shot on the neck would likely require stitching so there would be a very visible scar. Is it his privately-owned weapon? Depends on the jurisdiction if he has to report.